Process and apparatus for high energy efficiency chemical looping combustion

ABSTRACT

Process and apparatus are provided for a high energy efficiency chemical combustion process. The process provides two reaction steps, both of which are exothermic. First, a reduced oxygen carrier is contacted with oxygen in a reactor to form an oxidized oxygen carrier, such as metal oxide or metal suboxide, and then the oxidized oxygen carrier is fed to a second reactor and combusted with a fuel. The reaction produces the reduced oxygen carrier and carbon dioxide. The reduced oxygen carrier from the second reactor is recycled back to said first reactor. Carbon monoxide can also be produced during the process depending on stoichiometric amounts of the reactants. Though the process can be performed in various types of reactor systems, one preferred embodiment is the flash furnace with the production of fly ash during combustion. The process is highly efficient and produces a large amount of usable work.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of prior-filed U.S. ProvisionalPatent Application Ser. No. 61/255,716, filed on Oct. 28, 2009, thesubject matter of which is hereby incorporated by reference in itsentirety.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

The present invention was not developed with the use of any FederalFunds, but was developed independently by the inventors.

FIELD OF THE INVENTION

The present invention relates to apparatus and methods of highefficiency generation of useful work via combustion, more specifically,in combustion looping systems, for high efficiency energy production andmore particularly, the chemical looping combustion in furnaces of fuelsources using metal oxides. The invention relates to clean coaltechnology with carbon dioxide capture and sequestration. The inventionalso relates to the removal of fly ash produced during the combustionprocess that can be further utilized in ferroalloy processes.

BACKGROUND OF THE INVENTION

The burning of fuels is currently the main mechanism that the worldutilizes in order to meet its energy needs. Global warming is theincrease in the average temperature of the Earth's near-surface air andoceans. Global warming was first noticed in the mid-20th century andscientists have projected its continuation. The Intergovernmental Panelon Climate Change (IPCC) has noted that the global surface temperaturehas increased 0.74±0.18° C. (1.33±0.32° F.) during the last century. TheIPCC also concludes that although variations in natural phenomena suchas solar radiation and volcanoes produced most of the warming frompre-industrial times to 1950 and had a small cooling effect afterward,most of the observed temperature increase since the middle of the 20thcentury was caused by increasing concentrations of greenhouse gasesresulting from human activity such as fossil fuel burning anddeforestation. Although not unanimous, these basic conclusions have beenendorsed by more than 40 scientific societies and academies of science,including all of the national academies of science of the majorindustrialized countries. The basic argument that greenhouse gases keepthe Earth comfortably warm has never been challenged and it follows thatan increase in carbon dioxide in the atmosphere undoubtedly produces arise in temperature at ground level.

It is known that naturally occurring greenhouse gases have a warmingeffect by trapping heat radiated from the sun. The major greenhousegases are water vapor, carbon dioxide (CO₂), methane (CH₄), sulfurdioxide (SO₂) and ozone (O₃). Clouds also affect the radiation balance,but they are composed of liquid water or ice and so are consideredseparately from water vapor and other gases. CO₂ concentrations in theatmosphere are continuing to rise due to the continual burning of fossilfuels and land-use change.

Currently, the amount of carbon dioxide in the atmosphere is increasingat the rate of about one part per million per year. If this continues,some meteorologists expect that the average temperature of the earthwill increase by about 2.5 degrees Celsius. Such changes could be enoughto cause glaciers to melt, which would cause coastal flooding. Today theamount of carbon dumped globally into the atmosphere corresponds, onaverage, to one ton per person on the planet, each year. Becausecarbon-based energy is especially important in the United States, theaverage American per capita emission is 5 tons of carbon annually.

Among the fossil fuels, coal is the most carbon intensive so energygenerated by coal produces the highest carbon dioxide emissions. Coal isthe second largest domestic contributor to carbon dioxide emissions inthe United States. Currently about fifty percent of the energy in theUnited States is generated from coal, with more than 500 coal-firedpower plants in the United States. U.S. coal burning power plantscontribute 1.5 billion tons per year of carbon dioxide. Coal is found inabundance in various countries, including the Unites States, India andChina. The supply of coal in the United States is projected to last forup to 250 years. It is currently thought that coal will continue to beused to meet the world's energy needs in significant quantitiesthroughout the world because coal is plentiful and relatively lessexpensive than other energy producing technologies. Globally, coal isresponsible for 40% of carbon dioxide emissions. The InternationalEnergy Agency predicts that China will surpass the United States incarbon dioxide emissions by the end of 2009 and China continues to buildnew coal-fired power plants for its energy needs.

In 2006, environmental groups pushed for legislation that wouldreinstate CO₂ as a pollutant. In August of 2006, EPA General CounselRobert Fabricant concluded that since the Clean Air Act does notspecifically authorize regulation to address climate change, CO₂ is nota pollutant. Nonetheless, the public has become more concerned aboutglobal warming which has led to new legislation. US power plants facepressure to reduce CO₂ emissions. The coal industry has responded byrunning advertising campaigns touting clean coal in an effort to counternegative perceptions, as well as by putting more than $50 billiontowards the development and deployment of clean coal technologies,including carbon capture and storage. The expenditure has beenunsuccessful to date in that there is not a single commercial scale coalfired power station in the United States that captures and stores morethan token amounts of carbon dioxide.

European power plants are also faced with reducing their CO₂ emissionssignificantly by 2012 as required by the Kyoto Protocol. Energyproducers have embarked upon a unique way to reduce the CO₂ emitted intothe atmosphere via a technique known as carbon capture and storage whichinvolves siphoning off and burying the CO₂ underground. While the CO₂ isnot eliminated, it is contained. The Department for Environment Food andRural Affairs is working out plans to give industries credit for carboncapturing and storing in the second phase, from 2008-12, of the Europeancarbon trading scheme. Such technologies, however, also have potentialnegative effects on the environment, such as underground leaking,contamination of waters, and potential health effects on plants andanimals. Geological structures used to store carbon dioxide need to beable to remain stable and retain their capacity for hundreds or eventhousands of years. Thus, these technologies are in development andtesting and are not yet considered to be a final solution for carbondioxide reduction in the atmosphere.

Carbon capture and sequestration can reduce carbon dioxide emissionssignificantly, while allowing the use of coal as a fuel source. First,coal is collected in a gasifier with oxygen and steam where heat andpressure are used to form a synthetic gas, known as “syngas”. The carbondioxide can then be captured. The syngas is composed of carbon monoxideand hydrogen. Potential uses of syngas include power generation andfertilizers.

After being captured as a gas from the separation stage, the carbondioxide can be compressed to supercritical fluid and/or cooled todecrease its volume. Tankers, trucks and ships are used for bulktransport over short distances and in small to moderate scales. Forlarger plants, a pipeline is usually the practical alternative fortransportation of carbon dioxide.

The CO₂ can be sent to food production, such as incorporation into softdrinks or to the agricultural industry as a viable ingredient infeedstock, or it can be contained for geological storage.

Typical carbon dioxide sequestration technologies include coal beds,depleted oil and gas reservoirs, and saline aquafiers. Carbon dioxidecan also be dissolved in the ocean deeper than half a mile, or depositedon the sea floor more than two miles down in liquefied form.Unfortunately, some sequestration technologies are still subject topotential leaks into the environment with harmful consequences.Geological structures used to store carbon dioxide need to be able toremain stable and retain their capacity for hundreds or even thousandsof years. Thus, the optimal solution to the carbon dioxide problem is tominimize its emission.

In addition to CO₂. various other emissions are produced during fuelcombustion processes, including sulfur dioxide, nitrogen oxides andmercury. It has been found that these pollutants also promote thegreenhouse effect as well as the reduction of the ozone layer in thestratosphere. Extensive research of these emissions has been carried outin recent years.

Of course, the best alternative to avoid greenhouse effects and othernegative environmental consequences would be to find a way to eliminateor minimize the production of CO₂ and other pollutants during theprocess of power generation. Thus, a focus has developed on methods ofhigh efficiency energy production.

Clean coal technology is an umbrella term used to describe technologiesbeing developed that aim to reduce the environmental impact of coalenergy generation. These technologies include chemically washingminerals and impurities from the coal, gasification, treating the fluegases with steam to remove sulfur dioxide, carbon capture and storagetechnologies to capture the carbon dioxide from the flue gas anddewatering lower rank coals (brown coals) to improve the calorificquality, and thus the efficiency of the conversion into electricity.

Clean coal technology usually addresses atmospheric problems resultingfrom burning coal. Historically, the primary focus was on sulfur dioxideand particulates, since it is the most important gas in the causation ofacid rain. More recent focus has been on carbon dioxide. Concerns existregarding the economic viability of these technologies and the timeframeof delivery, potentially high hidden economic costs in terms of socialand environmental damage, and the costs and viability of disposing ofremoved carbon and other toxic matter.

The world's first “clean coal” power plant went on-line in September2008 in Spremberg, Germany. The plant is state-owned and has been builtby the Swedish firm Vattenfall. The plant is state owned because of thehigh costs of this technology. Private investors often invest in othersources of power such as nuclear, solar and wind power generationtechnologies. The facility captures carbon dioxide and acid rainproducing sulfides, separates them, and compresses the carbon dioxideinto a liquid state. It has been planned to inject the carbon dioxideinto depleted natural gas fields or other geological formations.

In conventional pulverized coal-fired power plants and Super CriticalPulverized coal technologies (SCPC) that produce flue gases, the carbondioxide is separated out of the flue gases. Typical CO₂ capture is inthe range of 80 to 95%. The flue gas is passed through an absorber wherea solvent removes most of the carbon dioxide. In Integrated GasificationCombined-Cycle technology (IGCC), which is utilized in newer powerplants and well suited for high grade bituminous coal, about 90% of theCO₂ is removed. Syngas is cooled and cleaned to remove particulates andother emissions. It is then combusted with air or oxygen to driveturbine engines. Exhaust gases undergo heat exchange with water andsteam to drive steam turbines and power generators.

A major disadvantage to IGCC technology and SCPC technologies are themajor technical modifications required for retrofitting existing powerplants, involving massive costs. In fact, engineering estimates show itmay prove that it would be less expensive to destroy existing powerplants and build new ones rather than to retrofit the existingfacilities. Such costs may thus prove prohibitive for implementing cleanair technology.

Another technology option for reducing carbon dioxide emissions isUnderground Coal Gasification (UCG). This technology however, presentsother environmental concerns associated with coal mining. Oxygen firedpulverized coal combustion appears to be more promising for lowerquality coals. The process involves burning coal in an oxygen-richatmosphere to produce a pure stream of carbon dioxide.

Chemical Looping Combustion (CLC) has presented itself as a viabletechnology for improved fuel combustion and power generation. Firstintroduced in 1954, in 1983 chemical looping combustion was presented asa way of increasing the thermal efficiency of power plants, and in the1990's, it was recognized as a possibility to capture carbon dioxidefrom fossil fuels in order to reduce climate impact. CLC is a combustiontechnology where no direct contact occurs between air and fuel. It is anemerging technology that enables carbon dioxide capture without the highefficiency loss of current carbon capture technologies.

The chemical looping combustion process for hydrocarbons or hydrogenbased fuels that has been developed to date is a process in whichmetal-based oxygen carriers undergo repeated reduction/oxidation cyclesto allow for combustion without the fuel coming into contact with air.In the simplest form of CLC, an oxygen carrying species, normally ametal or metal suboxide is first oxidized in air forming a metallicoxide. This oxide is then utilized as the oxygen source for theoxidation of the fuel material. In this step, the metal oxide is reducedback to the pure metal or suboxide using the hydrocarbon as reducer inthe second step of the reaction.

The two step reaction process provides two product streams, the first ofwhich contains carbon dioxide and water, wherein the carbon dioxide andminor impurities can be collected and sequestered for storage. Thereby,CLC enables the generation of power. The CLC system is composed of tworeactors, an air reactor and a fuel reactor. The fuel is introduced intothe fuel reactor, which contains a metal oxide. In the most commonprocess where methane is utilized, the exit gas stream from the fuelreactor contains CO₂ and H₂O. A stream of substantially pure CO₂ isobtained when H₂O is condensed. The reduced metal oxide is transferredto the air reactor where it is oxidized.

In one example of the prior art, a nickel-based system burning purecarbon would involve the two following redox reactions:

2Ni+O₂→2NiO   (1)

C+2NiO→CO₂+2Ni   (2)

When reactions (1) and (2) are combined, the reaction set reduces tostraight carbon oxidation with the nickel acting as a catalyst or oxygencarrier only:

C+O₂→CO₂   (3)

In chemical looping combustion of the prior art, the CO₂ is inherentlyseparated from other flue gas components, such as N₂ and O₂ and thus noenergy is expended for the gas separation and no gas separationequipment is needed. Depending on the metal oxide and fuel used,reaction (I) is often exothermic, while reaction (2) is endothermic. Thetotal amount of heat evolved from reactions (1) and (2) is the same asfor common combustion processes where the oxygen is in contact with thefuel.

In 2001, a design based on the circulating fluidized bed principle waspresented by Lyngfelt, Leckner and Mattison. Most of the work so far inchemical looping combustion has been directed to applications thatemploy a dual fluidized bed system where the fluidized beds areinterconnected. The metal oxide is in the form of particles employed asan oxygen carrier and bed material providing the oxygen for combustionin the fuel reactor. The reduced metal is then transferred to the secondfluidized bed (air reactor) and re-oxidized before being reintroducedback to the fuel reactor completing the loop.

In the processes of the prior art, the metal oxide or metal suboxide istypically placed on a ceramic support material, for example NiAl₂O₄, andthis material is processed in dual fluid bed type reactor systems in apelletized form. Besides nickel oxide, iron, manganese and copper oxideshave been evaluated. For example, the National Energy TechnologyLaboratory carried out an evaluation of these metal oxides using ahigh-pressure flow reactor at 150 psi with synthesis gas and found thatthey showed a stable reactivity over three high-pressure cycles. Theteam concluded that though direct coal combustion is feasible with metaloxides, it would be necessary to develop an efficient solid circulationprocess and ash/metal-oxide separation process.

The prior art focuses on the development of suitable oxygen carriersupports or binders for the process. The ability of the oxygen carriersupports to convert a fuel gas fully to CO₂ and H₂O has beeninvestigated thermodynamically. For example, U.S. patent applicationSer. No. 11/010,648 to Thomas et al. discloses a method for producinghydrogen gas which comprises reducing a metal oxide in a reductionreaction between a carbon-based fuel and a metal oxide to provide areduced metal or metal oxide having a lower oxidation state, andoxidizing the reduced metal or metal oxide to produce hydrogen and ametal oxide having a higher oxidation state. The metal or metal oxide isprovided in the form of a porous composite of a ceramic materialcontaining the metal or metal oxide.

Many types of oxygen carrier supports or binders have been studies,including zirconia, alumina, metal aluminate spinels, titanium dioxide,silica, and kaolin clay. Yttriated zirconia remains the supportconsidered to be the most efficient because it acts as an ion conductorfor the O²⁻ ions at the working temperatures and thereby increases thereactivity of the redox system. A number of patents disclosecerine-zirconia type oxides in the field of the process using a redoxactive mass in a circulating bed process, including in chemical loopingcombustion.

A common problem with all transitional metal oxygen carriers is theformation of carbon deposits (i.e. coke) on the surfaces of carrierparticles during the reduction phase. M. Ishida and H. Jin have reportedthat carbon deposits cause degradation of the physical strength of theparticles and their chemical stability.

In conventional CLC, the bulk of the power is generated by the hot fluegas from the air reactor entering a gas turbine. Thus, a power plant'soverall thermal efficiency is highly dependent on the maximumtemperature that can be tolerated by the carrier during oxidation forextended periods. Sensitivity analysis shows that thermal efficiencyvaries with an increase in temperature of the reaction. It is currentlythought that to achieve greater efficiencies, appropriate metal oxygencarrier supports are required.

The arrangement of a reversible CLC engine is based on receiving heat athigh temperature from the exothermic oxidation reaction. Part of thisenergy can be converted into work; the rest is utilized as heat. Almostall of that heat can be absorbed by the endothermic reduction reaction.Therefore, this arrangement requires the redox reactions to beexothermic and endothermic respectively.

U.S. Pat. No. 5,447,024 to Ishida et al. discloses a chemical loopingcombustion system utilizing the following formulae (1) and (2).

RH+MO→mCO₂+nH₂O+M   (1)

M+0.5O₂→MO   (2)

The reduction product (M) of metallic oxide (MO) obtained according toformula (1) is utilized in the oxidation reaction of formula (2).Therefore, a chemical looping reaction occurs with MO as an oxygencarrier. The reaction of the formula (1) is an endothermic reaction ofthe metallic oxide (MO) and a fuel (RH) with low-energy absorption in alow-temperature region (about 600-1,000 K). The reaction of the secondformula (2) is an exothermic oxidation reaction of the product (M) ofthe first step in a high-temperature region (about 800-1,700 K). Ahigh-temperature exhaust gas is produced by the heat of the reaction andis utilized for driving a gas turbine. The product (M) is exemplified bymetals such as iron, nickel, copper and manganese. The patented processuses circulating bed technology to allow continuous change of the activemass from the oxidized state to the reduced state.

The patent claims as the active mass the use of the redox pair NiO/Ni,alone or associated with binder YSZ (defined by zirconia stabilized byyttrium). The advantage of the binder in the process is the increase ofthe mechanical strength of the particles. The particles would be tooweak to be used in a circulating bed when NiO/Ni is used alone.

FIGS. 1 and 2, demonstrate the CLC process of the prior art utilizingNiO, Mn₃O₄, Fe₂O₃ and other oxides. The figures demonstrate thatreaction (2) is highly exothermic with adiabatic temperatures exceeding3000° C. Such high temperatures make it difficult to control andmaintain the temperature in the fluidized bed reactor below the meltingpoint of either the metal oxide or the metal. In addition, in order toavoid forming sintered build-ups, good temperature control and coolingis required, lack of which in the prior art processes results inincreased heat losses from the process. The endothermic step of thesetwo reactions consumes substantial energy from the exothermic reactionstep and this heat transfer cannot be realized with zero heat loss. As aresult, the thermal efficiency of the chemical looping combustionprocesses of the prior art is poor and a process for improved thermalefficiency is needed.

Heat transfer and endothermicity of reaction are also substantialproblems in various other industrial processes. In the industrialprocess known as steam reforming, hydrogen is produced by passing steamand a hydrocarbon through a nickel catalyst. Other processes include thegasification of biomass, the catalytic reforming of petroleumhydrocarbons, the decomposition of methanol. G. P. Curran, C. E. Fink,and E. Gorin in an article entitled CO₂ Acceptor Gasification Process,in Fuel Gasification, suggest the reaction: CO₂+CaO═CaCO₃. The reactionis highly exothermic, thereby supplying the heat consumed by theendothermic gasification reaction. Furthermore, CO₂ and CO are inequilibrium via the water shift reaction: H₂O+CO═CO₂+H₂. Consequently,removing the CO₂ has the effect of also removing the CO, allowing theproduction of a gas containing a large mole fraction of hydrogen. Theauthors conclude, however, that for this process to be practical, it isnecessary to reconvert the CaCO₃ back to CaO. The heat necessary to dothis can be readily generated by burning some fuel; however,transferring the heat to where it is needed within the reactor system isa difficult and expensive problem. Thus, these processes of the priorart leave a need for a new method of burning fuel which allows for moreeffective energy generation, better heat transfer and reduced heatlosses.

The majority of the work performed to date on chemical loopingcombustion has been performed using methane and coal as the fuels ofchoice. Current CLC processes operate most effectively with a gaseousfuel material such as methane. Solid fuel material CLC processing ofcoal is desirable but is less effective due to the restrictions of thesolid to solid reactant mass transfer limitations of the process. Inaddition, when processing coal as the fuel material, the oxygen carrierbecomes “poisoned” over time by the non-combustible mineral componentscontained in the coal, known as fly ash. This contamination affects thereactivity and porosity of the heterogeneous oxygen carrier systemrendering the metal oxide and support ceramic unusable. When the oxygencarrier is depleted, the pelletized oxygen carrier material must beremoved from the fluid bed reactor for reprocessing. At that point, thevaluable metal oxide must be separated from the substrate or supportceramic. Rejuvenation of the metal oxide and separation and recovery ofthe substrate ceramic waste components is a costly process which has anadverse impact on the overall cost of the CLC processes of the priorart.

Limited studies have been performed with oxygen carriers used to combustliquid fuels. The application for CLC for power production for liquidfuels such as heavy hydrocarbons is gaining wide interest in the oil andrefining industry. The use of liquid fuels raises specific problems ofimplementation that are different than for gas or solids.

The largest, a 50 kW, chemical looping combustion system in operation asof 2008 was been built in Korea and operated continuously for 25 hours.In Europe, current experience is from a 10 kW CLC facility located inChalmers University of Technology in Sweden. The Technical University ofVienna in Austria is working on scaling-up its CLC process. Thesevarious CLC facilities implement the known developed variables and eachprocess implements various trade-offs between efficiency, carbon dioxidecapture and oxygen carrier properties.

Therefore, despite the progress in CLC technology, the world stilldesires an energy generation process that is highly efficient and canreduce the emission of unwanted side products while being economicallypractical to operate. The process and apparatus of the present inventiontake us one step closer to the desired solution.

The above and other features of the invention, including various noveldetails of construction and combination of parts, will now be moreparticularly described with reference to the accompanying drawings andpointed out in the claims. It will be understood that the particularreactions and apparatus embodying the invention are shown by way ofillustration only and not as a limitation of the invention. Theprinciples and features of the invention may be employed in various andnumerous embodiments without departing from the scope of the invention.

SUMMARY OF THE INVENTION

An object of the present invention is the generation of useful work. Theimprovement over the prior art is that both reaction steps of theprocess are exothermic and useful work is generated during exothermicchemical looping combustion conditions in both reactions steps of theprocess. Embodiments of the present invention address the need for ahigh efficiency energy generation process by providing a process forchemical looping combustion comprising contacting a reduced oxygencarrier with oxygen to form an oxidized oxygen carrier, and contactingsaid oxidized oxygen carrier and a fuel to produce said reduced oxygencarrier and carbon dioxide, wherein both steps of the process areexothermic. During the process, the steps can be performed in eitherorder within the furnace.

In accordance with one embodiment of the present invention, the processfor chemical looping combustion is performed in a furnace and comprisesa first step wherein a reduced oxygen carrier is contacted with oxygento form an oxidized oxygen carrier, and a second step wherein anash-containing fuel is contacted with said oxidized oxygen carrier toproduce a reaction product comprising said reduced oxygen carrier,carbon dioxide and fly ash. Both the first step and the second step areexothermic.

One preferred embodiment of the present invention provides a process forchemical looping combustion in a flash furnace. The flash furnacecomprises a first reactor and a second reactor receivably connected tothe first reactor. The process comprises the steps of: (a) feedingoxygen and a reduced oxygen carrier into the first reactor having afirst reactor temperature at a location that is not a reaction zone, theoxygen and the reduced oxygen carrier each having a temperature that islower than the first reactor temperature, and the first reactortemperature being sufficient to ignite the oxygen and the reduced oxygencarrier as they pass through the first reactor and create a reactionthat is sufficiently exothermic to form a self-sustaining reaction zonehaving a first flash temperature, said reaction producing an oxidizedoxygen carrier; (b) feeding the oxidized oxygen carrier and a fuel intothe second reactor at a location that is not a reaction zone having asecond reactor temperature, the oxidized oxygen carrier and fuel eachhaving a temperature that is lower than the second reactor temperature,and the reactor temperature being sufficient to ignite the oxidizedoxygen carrier and the fuel as they pass through the second reactor andcreate a reaction that is sufficiently exothermic to form aself-sustaining reaction zone having a second flash temperature, thereaction producing the reduced oxygen carrier and carbon dioxide; and(c) optionally, feeding the reduced oxygen carrier from the secondreactor to the first reactor.

BRIEF DESCRIPTION OF THE DRAWINGS

In order that the manner in which the above-recited and other advantagesand objects of the invention are obtained, a more particular descriptionof the invention will be rendered by reference to specific embodimentsthereof which are illustrated in the appended figures.

FIG. 1 is a graph showing the enthalpy change for reduction reactionswith carbon.

FIG. 2 is a graph showing the enthalpy change for reduction reactionswith methane.

FIG. 3 is a diagram flowsheet of the high thermal efficiency chemicallooping combustion process of the present invention.

FIG. 4 is a graph showing the enthalpy change for reduction reactionswith hydrogen.

FIG. 5 is a graph showing of the thermal decomposition of MoO₃ accordingto the process of the present invention.

FIG. 6 is a graph showing the equilibrium composition for the reductionof MoO₃ with a stoichiometric amount of carbon according to the processof the invention.

FIG. 7 is a graph showing the thermal decomposition of Na₂O₂.

FIG. 8 is a graph showing the thermal decomposition of MnO₂.

FIG. 9 is a graph showing the thermal decomposition of Rh₂O₃.

FIG. 10 is a graph showing the thermal decomposition of PdO.

FIG. 11 is a graph showing the thermal decomposition of PtO.

FIG. 12 is a graph showing the thermal decomposition of NiO.

FIG. 13 is a graph showing the thermal decomposition of V₂O₅.

FIG. 14 is a graph showing the thermal decomposition of TlO₃.

FIG. 15 is a graph showing the thermal decomposition of OsO₄.

FIG. 16 is a graph showing the thermal decomposition of Re₂O₇.

FIG. 17 is a graph showing the thermal decomposition of Tc₂O₇.

FIG. 18 is a graph showing the thermal decomposition of CuO.

FIG. 19 is a graph showing the thermal decomposition of BaO₂.

FIG. 20 is a graph showing the equilibrium composition for the reductionof carbon dioxide with carbon.

DETAILED DESCRIPTION OF THE INVENTION Furnaces

The process of the invention is particularly suited in the environmentof chemical looping combustion systems. Without limiting theapplicability of the invention, the invention will be specificallydescribed in the environment of chemical looping combustion. The processof the current invention may be carried out in various types ofcombustion systems, including rotary kilns, multiple hearth furnaces,vertical tube furnaces or fluidized bed reactors.

With reference to FIG. 3, in a preferred embodiment, the process iscarried out in a flash furnace. The flash furnace utilized for theprocess of the invention will contain at least two separate reactionvessels, herein referred to as “reactors”, though more reactors may beappended.

The temperature of one reactor may vary from the temperature of thesecond reactor. The term “reactor temperature” as used herein refers tothe temperature of a reactor at any particular time at the locationwithin the reactor where the reactants are being fed into the reactor.It is preferred that the reactants be fed into the reactor at the top ofthe furnace, such that the reactants fall gravitationally through thefurnace and react with one another as they are falling. As the reagentsbegin and continue to react within the reactor, the temperature withinthe reactor will increase. The reactants will then enter the flash zonewhere the reaction will proceed to its completion.

Therefore, in a preferred embodiment of the process of the invention,the reduced oxygen carrier flows concurrently in the same direction withthe flow of the oxygen in the first reactor. Similarly, in the secondreactor of the furnace, the oxidized oxygen carrier flows concurrentlyin the same direction with the flow of the fuel. The concurrent flow ofthe process increases the contact time between the reactants, therebyincreasing the kinetics of the reaction and ensuring completion of thereaction. Concurrent flow also enables control of the oxygen carrier tofuel ratio within the process thereby increasing the accuracy of thereagent ratio in the process of the invention.

Flash

Embodiments of the invention provide a high thermal efficiency CLCprocess wherein substantial energy is generated during both reactionsteps of the process. Each reaction creates a sufficiently exothermicreaction having a stable flash reaction zone in which these reactionsproceed to their completion. The term “flash” or “flash zone” will beused herein to refer to a reaction zone that is self-sustaining and hasa high temperature as a result of the reactants coming into contact withone another in the reactor. As used herein, the term “flashtemperature”, as distinguished from “reactor temperature”, refers to thehighest temperature of the reaction in the flash zone of the reactor.

For practical purposes of operation of the flash furnace, it ispreferred that the length of the reactor be sufficiently long to allowsome differential between the reactor temperature and the flashtemperature so that the reactants can have at least a few seconds tofall through the reactor before the flash is created within the reactor.In one embodiment of the process, the fuel and the oxidized oxygencarrier are blended prior to being passed into the second reactor. Theblending can be carried out by various mixing or blending processescommonly known and commercially available for such industrial processes.

Continuous Process

The preferred process is continuous in that the reduced metal oxide ormetal suboxide is recycled back in a loop into the system, hence theterm “looping”. The oxygen carrier can be recycled in its' heated statefrom the second reactor, which will further facilitate the formation ofa stable flash in the reactor. In order to optimize the continuity ofreaction, in a preferred embodiment, the oxygen and the reduced oxygencarrier are fed into the first reactor at a rate that is substantiallyconstant while the first and the second reactor are, respectively,maintained at substantially constant temperatures.

Oxygen Carriers

The exothermic conditions of the process of the invention can beachieved by carefully choosing the appropriate oxygen carrier and uniqueoperating conditions in a way that both reactions (1) and (2) becomehighly exothermic. By the term “reduced oxygen carrier” as used hereinis meant a metal or a metal suboxide. The term “oxidized oxygen carrier”as used herein refers to an oxygen carrier that has been oxidized suchthat it has a higher oxidation state than the reduced oxygen carrier.The term “oxygen carrier” is used herein to refer to either reducedoxygen carrier or oxidized oxygen carrier.

The preferred reduced oxygen carriers of the invention are rhenium,platinum, rhodium, palladium, copper, barium, manganese, molybdenum,vanadium, bismuth, lead, mercury, sodium, potassium, rubidium, andcesium.

One embodiment of the invention is a process wherein more than oneoxygen carrier is utilized at the same time within the furnace. Apreferred embodiment of such a process is the combination of MoO₃ andRe₂O₇.

In contrast to the prior art, the oxygen carrier within the process ofthe invention is substantially free-flowing. By “free-flowing”, it ismeant that the oxygen carrier is not supported on a binder material ofany sort, such as the ceramic supports of the prior art. When coal isreacted with a heterogeneous system, where the oxygen carrier is boundto a substrate, it becomes challenging to completely burn the fuel dueto the difficulty in providing direct physical contact between thereagent particles.

In addition, virtually no vapor pressure is created over the oxygencarrier systems of the prior art, as can be seen for example in FIG. 12for NiO in the temperature range of 100-1500° C. The oxidation reactionproceeds solely in a solid state. In the improved process of theinvention, the free-flowing reactants flow co-currently while the oxygencarrier acting as oxidizing agent develops a tangible vapor pressure.The vapor greatly facilitates the mass transfer and kinetics andultimately leads to complete fuel combustion. Creating such uniquekinetic conditions for the CLC process of the invention also leads tothe removal of the volatile impurities, such as mercury, sulfur andothers. Thus the CO₂, SO₂. and Hg are removed in highly concentratedform for capture and sequestration. It is also important to note thatproduction and emission of nitrogen oxides are dramatically reducedduring the fuel combustion process of the invention.

It is relevant to note that the nickel oxide used in the CLC processesof the prior art presents well-known serious health and environmentalproblems. Among the oxides that can be used in the improved CLC processof the present invention, lead, mercury and some other compounds presenta clear hazard. Therefore, preferred are oxides and/or metals that donot present serious health problems. These are molybdenum, vanadium,bismuth, platinum, rhodium, and palladium oxides, though due to theirhigh cost, platinum, rhodium and palladium are less preferred.

Preferably, the oxygen carrier particles used in the process of theinvention are in powder form. By “powder” is meant a solid substancethat is in a state of fine, loose particles. The powder form of theoxygen particles can be obtained by crushing, grinding, disintegration,or other mechanisms. Preferably, the oxygen carrier has a particle sizeof from 100 nanometers to 1 mm as determined by laser light scattering.More preferably, the oxygen carrier is in the form of a powder having aparticle size of from 20 microns to 250 microns as determined by laserlight scattering.

In order for the materials to be accepted for use in the CLC process ofthe invention, it is desirable that the oxide/suboxide or oxide/metalpairs meet the following criteria: (1) both reactions must beexothermic; (2) the reduced oxygen carrier must generate enough gaseousspecies to promote the oxidation of a solid fuel such as coal; and (3)the re-oxidation of the suboxide/metal with air at atmospheric pressuremust be thermodynamically feasible.

Tables 11-13 of the Examples and FIGS. 7-19 reflect the correspondenceof various oxide/suboxide and oxide/metal pairs that meet the outlinedcriteria of the invention. Various oxygen carriers can be chosen forreaction with fuel in the chemical looping combustion process of theinvention. For example, rhenium (VII) oxide is a volatile compound andits reaction with fuel is exothermic (see Table 11).

It can be seen from FIGS. 14, 15 and 17 that the oxides of Tl, Os, andTc become volatile at low temperatures which make them practicallyimpossible for processing. On the contrary, the vanadium pentoxide (FIG.15) is thermally quite stable and may be difficult to use for theoxidation of a solid fuel such as coal. For comparison, the nickel oxide(FIG. 13) normally used in the traditional CLC processes of the priorart exhibits the same thermal pattern.

Vaporization

In another embodiment of the invention, the oxygen carrier is at leastpartially vaporized in the furnace. In a process where coal is utilizedas the fuel in the reaction, a substantial vapor phase in the reactor isimportant to create the exothermic reaction of the solid coalparticulate in order to maintain the high-temperature flash conditionsand the stability of the flash. The reactions can therefore be driven totheir completion using near stoichiometric amounts of the reagents. Onthe contrary, carrying out the reduction of the metal oxides in either arotary kiln or a fluidized bed reactor requires a large excess of onereagent and/or long retention time due to mass transfer limitations thatmake it difficult to achieve complete reaction.

Other embodiments of the invention include processes wherein thetemperature within the first reactor is above the solid/liquid phasetransition temperature of the reduced oxygen carrier; the temperaturewithin the first reactor is above the solid/gas phase transitiontemperature of the reduced oxygen carrier; the temperature within thefirst reactor is above the liquid/gas phase transition temperature ofthe reduced oxygen carrier; the temperature within the second reactor isabove the solid/liquid phase transition temperature of the oxidizedoxygen carrier; the temperature within the second reactor is above thesolid/gas phase transition temperature of the oxidized oxygen carrier;or the temperature within the second reactor is above the liquid/gasphase transition temperature of the oxidized oxygen carrier.Volatilization of the oxygen carrier reagents will create superior masstransfer of the oxygen carriers and promote the reaction kinetics. Thisadvantage will promote the completion of the reactions while allowingfor a reduction in the need for a large excess availability of theoxygen carrier materials. These phase changes can be identified by thechange in enthalpy values, such as those set forth in the tables withinthe Examples of the invention hereinbelow.

In chemical looping combustion, isolation of the fuel from airsimplifies the number of chemical reactions in combustion. According toa preferred embodiment of the process of the invention, employing oxygenin the oxygen carrier without nitrogen and the trace gases found in airwill eliminate the primary source for the formation of nitrogen oxide(NO_(x)), producing an off gas composed primarily of carbon dioxide andwater vapor. Such a rich gas stream high in CO₂ is a great advantage forcarbon capture technologies.

Temperature Conditions

Using as an example a nickel-based system, burning pure carbon involvesthe following reactions, with ΔG signifying a change of Gibbs freeenergy:

2Ni+O₂→2NiO (−ΔG₁)

C+2NiO→CO₂+2Ni (−ΔG₂)

C+O₂→CO2 (−ΔG₃)

According to the 1^(st) and 2^(nd) laws of thermodynamics, the maximumamount of work that a system can produce is equal to the change of freeGibbs energy for reaction (3)—(−ΔG₃). This statement is true providedthermodynamically reversible conditions exist for reactions (1) and (2).It is practically impossible to carry out the process at thermodynamicequilibrium at each given time/intermediate composition. Therefore,according to the 2^(nd) law of thermodynamics, the actual amount ofuseful work will be always less than −ΔG₃. As only one exothermicreaction is used to produce useful work in the chemical loopingcombustion processes of the prior art, the useful work of the prior artCLC processes cannot exceed −ΔG₂. In order to get closer tothermodynamically reversible conditions and maximum useful work, theheat losses for reactions (1) and (2) should be minimized. In apreferred embodiment, the creation of adiabatic conditions (zero heatlosses) within the reaction process would bring the theoreticaltemperature conditions of the reaction closer to thermodynamicreversibility.

In order to minimize heat losses, retention of temperature through“looping” of the oxygen carrier or preheating of the reagents willfurther promote stability of the flash in each reactor. Therefore,“looping” steps 1 and 2 will create an opportunity to charge heatedmetal oxides and suboxides or metals into the furnace further increasingthe thermal efficiency of the system. Therefore, in a preferredembodiment of the process, the reactants can be preheated before beingfed into the reactor, though preferably to a temperature that is lowerthan the flash temperature. Thus, the reduced oxygen carrier and theoxygen can be preheated before being fed into the first reactor of thefurnace and the fuel and the oxidized oxygen carrier can be preheatedbefore being fed into the second reactor of the furnace.

Carrying out the process at higher temperatures will greatly increasethe rate and the completion of the reactions. This opportunity simplydoes not exist for the processing of NiO, Fe₂O₃ and Mn₃O₄ oxygencarriers utilized in the processes of the prior art as these firstreactions are endothermic (see FIGS. 1 and 2).

Another means for controlling the temperature conditions within thefurnace is by controlling the amount of reagent fed into the system. Ina preferred embodiment, the reduced oxygen carrier and the oxygen arefed into the first reactor at a rate sufficient to substantially off-setthe heat loss of the first reactor and create a flash; and the oxidizedoxygen carrier and the fuel are fed into the second reactor at a ratesufficient to substantially off-set the heat loss from the secondreactor and create a flash.

Residence Time

Due to the short residence time in the flash furnace, the oxygencarriers in either the first or the second step will have little or notime to agglomerate, and therefore, will have high surface area. Sincethe oxygen carriers will be free flowing and their bulk densities willbe lower than those of agglomerated oxygen carriers. As a result, theresidence time in the flash will increase and will work to drive thechemical reactions to their completion. In the preferred embodiment ofthe process under desired reaction conditions within a flash furnace,the process of the residence time of the oxygen and the reduced oxygencarrier in the first reactor being from 0.01 to 1.0 minute, and morepreferably, from 0.01 to 10 seconds. Similarly, the residence time ofthe fuel and the oxidized oxygen carrier in the second reactor is from0.01 seconds to 1.0 minute and preferably from 0.01 seconds to 10seconds.

According to the invention, drastic reduction of the residence time andthe oxygen carrier gas volume in the first step of the process willfacilitate a dramatic reduction of the heat losses of the process in aflash furnace thereby allowing more energy to be converted into usefulwork.

Fuel

Many types of fuel can be utilized in the process of the invention, suchas carbon, coal, hydrogen, hydrocarbon, biofuel, methane, natural gas,petroleum, crude oil, tar sands, oil shale, biomass, algae, fuel-richwaste gases from fuel cells and other fossil fuels and synthetic fuels.Various types of fuels may be combined during the process. Furthermore,the invention is not limited by the physical characteristics of the fuelbeing in a solid, liquid or gas phase, although embodiments havingsmaller particle sizes are preferred. It has been found that where thefuel is a carbon, a hydrocarbon, or hydrogen, it can be fed into theprocess and apparatus of the invention in the form of a solid, a liquidor a gas.

For solid fuels, the process will be optimized if the fuel is fed intothe reactor in a powder form. By “powder” as used herein is meant that asolid fuel source is first pulverized such that it creates free-flowingparticles. In a preferred embodiment, the coal powder has a particlesize of from 100 nanometers to 10 mm as determined by laser lightscattering, and more preferably the coal powder has a particle size offrom 20 microns to 250 microns as determined by laser light scattering.In one preferred embodiment of the process, particle size of the coalpowder is substantially similar to the particle size of the oxygencarrier in order to optimize reaction kinetics.

Fly Ash

When a fuel that contains ash is utilized in the process, fly ash isproduced during the process. As used herein, the term “fly ash” refersto non-combustible mineral components in the off-gas stream of theprocess. The fly ash produced from the burning of pulverized coal in atypical coal-fired boiler is a fine-grained, powdery particulatematerial that is carried off in the flue gas and usually collected fromthe flue gas by means of electrostatic precipitators, bag-houses, ormechanical collection devices such as cyclones. The chemical propertiesof fly ash are influenced to a great extent by those of the coal burnedand the techniques used for handling and storage. There are four maintypes, or ranks, of coal, each of which varies in terms of its heatingvalue, its chemical composition, ash content, and geological origin. Inaddition to coal, ash-containing fuels include crude oil, tar sands, oilshale and natural gas.

Dealing with fly ash is a major obstacle to overcome when burning coal.The fly ash accumulates over time on the surface of the oxygen carriercausing the oxygen carrier to lose its effectiveness. Eventually, theoxygen carrier becomes unusable for further processing because itbecomes practically impossible to either oxidize or reduce the compound.

Therefore, the oxygen carrier should be constantly or periodicallyremoved from the reaction and the reaction compensated with pure oxygencarrier at the same time to avoid deleterious level of contamination. Inone embodiment of the process of the invention, the reduced oxygencarrier and the fly ash are continuously removed from the furnace.Continuous removal of fly ash keeps the furnace free of build up andmaintains the integrity of the process. In order to keep the process incontinuous looping, substantially the same amount of reduced oxygencarrier that is removed from the furnace is fed back into the furnace,thereby maintaining the same reaction rates and flash temperatureswithin the reactors.

In traditional CLC processes, the material contaminated with fly ash iseither considered a loss or requires costly re-processing to separatethe metal or metal oxide from the support material and recover thevaluable metal components. In the process of the invention, especiallywhen processing oxides of molybdenum and vanadium, the material removedfrom the furnace is a mixture of fly ash together with the reducedoxygen carrier. The removed material can be utilized as an alloyadditive in steel or ferroalloy production, particularly in a process toproduce an alloy material containing iron and slag, includingferroalloys such as ferrovanadium, ferromolybdenum and ferromanganese.Since the oxygen carrier is a homogeneous free-flowing material withoutany binder or substrate support, no separation step is required. Takingout the homogeneous free-flowing oxygen carrier in a suboxide form fordirect sale will also result in a reduced reagent usage in the alloyproduction field. As a result, coal combustion via the improved CLCprocess of the invention will become even more economically attractiveas compared to prior art processes having supported oxygen carriersystems.

Carbon Dioxide and Carbon Monoxide

The gaseous products of the combustion process of the invention will becomprised of CO₂, CO and H₂O. Carbon monoxide is a chemically reactivegas that can be used for the production of a variety of chemicals, likemetal carbonyls, phosgene and array of organic compounds such asmethanol and other alcohols, formic and other organic acids, and theirderivatives. According to an embodiment of the invention, the carbonmonoxide can be separated and carbon dioxide can be substantiallyseparated, captured and sequestered.

The prior art fluidized bed technology is well known for generatinglarge amounts of dust during the combustion process. The off-stream ofthe endothermic reaction is comprised not only of CO₂ but also oftangible amounts of carbon. Excess amounts of carbon are required by theprocesses of the prior art at least in part due to their use ofsupported oxygen carriers of undetermined particle sizes. As shown inFIG. 20, as the temperature of the off-gas of the reaction changes, theCO₂ and carbon do not remain chemically inert to each other, andconsequently a small amount react to generate an appreciable amount ofCO. The amount of CO cannot be controlled nor calculated because thetemperature of the off-stream gas is unstable. As a result, the presenceof CO within the CO₂ stream, especially in unknown ratios, presents achallenge for the separation and sequestration of carbon dioxide. HighCO levels may be desired for production of carbon containing chemicals.CO can be desired over CO₂ due to its significantly higher chemicalreactivity.

In one embodiment of the invention, in order to produce a substantiallypure stream of CO₂ during the process of the invention, the fuel and theoxidized oxygen carrier are fed into the second reactor in substantiallystoichiometric amounts in order to produce an excess of carbon dioxideover carbon monoxide. In a process where the fuel and the oxidizedoxygen carrier are fed into the second reactor in less thanstoichiometric amounts, larger quantities of carbon monoxide will beproduced.

It has also been discovered herein that another means of controlling theproduction of CO₂ and CO involves the use of the following chemicalreaction:

CO₂(g)+C=2CO(g)

K═(P_(CO))²/(P_(CO2))

wherein K is the equilibrium constant at a given temperature and K is afunction of temperature solely and P is the partial pressure of thecorresponding gaseous species (CO and CO₂ respectively). Adding CO₂ gasto the system at a given temperature will cause an increase in thepartial pressure of CO according to the above equation for theequilibrium constant. In the event that the CO₂ gas is injected into thefurnace at the location of the flash, wherein the CO₂ gas has atemperature significantly lower than the flash temperature, thetemperature of the flash will be decreased. This will cause a change inthe equilibrium constant. As a result, the partial pressure of CO maydecrease (depending on the decrease of temperature.) Therefore, theamount of CO produced can be controlled not only by the partial pressureof the CO₂ gas in the flash zone but also by the flash temperature whichcan be changed by the amount of the CO₂ gas added to the flash zone. Inthis manner, it is hereby possible to control the CO₂/CO ratio andproduction of the CO₂ and CO.

EXAMPLES

The following examples illustrate the process and are intended to bepurely exemplary of the use of the invention and should not be viewed aslimiting its scope. In the tables below, T (in degrees Celsius)indicates the reaction or reactor temperature within the furnace. ΔHindicates the enthalpy change of the reaction, ΔS is the entropy changeof the reaction and ΔG is the change in Gibbs free energy. K is theequilibrium constant of the reaction at the given temperature. Thevalues of the examples were calculated using HSC CHEMISTRY® for WindowsThermodynamic Software by Outokumpu Research Oy of Finland.

Negative ΔG values in the tables below signify that the equilibrium ofthe reaction is shifted toward the right, i.e. toward formation of theproducts. The greater the value of the negative ΔG, the more completethe reaction, such that there would be an insignificant amount ofreactants left in the product of the reaction, which is also indicatedby the extremely high K values. The negative ΔH values in the tablesindicate that the reactions are exothermic.

Example 1

Molybdenum was used as the metal and reacted with oxygen to formmolybdenum trioxide as the oxidized oxygen carrier. Table 1 demonstratesthe thermodynamic analyses of the chemical looping combustion process ofthe invention using molybdenum trioxide with the following combustionreaction: 2MoO₃+C=2MoO₂+CO_(2(g))

TABLE 1 T ΔH ΔS ΔG C kcal cal/K kcal K 100.000 −19.277 34.432 −32.1266.565E+018 200.000 −19.412 34.113 −35.552 2.649E+016 300.000 −19.57733.797 −38.948 7.124E+014 400.000 −19.802 33.437 −42.310 5.469E+013500.000 −20.095 33.033 −45.634 7.956E+012 600.000 −20.453 32.597 −48.9161.757E+012 700.000 −20.877 32.139 −52.153 5.169E+011 800.000 −21.36031.667 −55.343 1.870E+011 900.000 −45.876 8.910 −56.329 3.122E+0101000.000 −47.006 7.984 −57.172 6.531E+009 1100.000 −48.010 7.225 −57.9311.663E+009 1200.000 −48.880 6.613 −58.622 4.984E+008 1300.000 −49.6096.134 −59.258 1.710E+008 1400.000 −50.190 5.775 −59.852 6.587E+007I500.000 −50.616 5.527 −60.417 2.801E+007

Example 2

Vanadium pentoxide was used as the reduced oxygen carrier and reactedwith oxygen as follows: V₂O₅+C═V₂O₃+CO₂(g). Table 2 demonstrates thethermodynamic analyses of the CLC process of the invention usingvanadium pentoxide.

TABLE 2 T ΔH ΔS ΔG C kcal cal/K kcal K 100.000 −14.618 42.080 −30.3205.746E+017 200.000 −14.573 42.187 −34.533 8.963E+015 300.000 −14.55342.227 −38.755 6.011E+014 400.000 −14.587 42.172 −42.976 8.994E+013500.000 −14.710 42.005 −47.186 2.184E+013 600.000 −14.957 41.706 −51.3727.237E+012 700.000 −30.684 25.207 −55.215 2.518E+012 800.000 −31.25324.651 −57.707 5.664E+011 900.000 −31.786 24.175 −60.147 1.607E+0111000.000 −32.284 23.768 −62.544 5.461E+010 1100.000 −32.744 23.420−64.903 2.142E+010 1200.000 −33.165 23.124 −67.230 9.435E+009 1300.000−33.543 22.875 −69.529 4.573E+009 1400.000 −33.874 22.671 −71.8062.400E+009 1500.000 −34.156 22.507 −74.065 1.348E+009

Example 3

Table 3 sets forth the thermodynamic analyses of methane gas usingmolybdenum trioxide as the reduced oxygen carrier with the followingreaction formula: 4MoO₃+CH₄(g)=4MoO₂+CO₂(g)+2H₂O(g)

TABLE 3 T ΔH ΔS ΔG C kJ J/K kJ K 100.000 −176.034 279.607 −280.3701.780E+039 200.000 −176.182 279.264 −308.316 1.097E+034 300.000 −176.765278.165 −336.196 4.387E+030 400.000 −178.059 276.101 −363.917 1.743E+028500.000 −180.146 273.224 −391.389 2.785E+026 600.000 −183.023 269.734−418.541 1.098E+025 700.000 −186.645 265.814 −445.321 8.035E+023 800.000−190.942 261.616 −471.695 9.147E+022 900.000 −396.477 70.843 −479.5862.267E+021 1000.000 −406.413 62.709 −486.251 8.944E+019 1100.000−415.364 55.936 −492.173 5.295E+018 1200.000 −423.266 50.377 −497.4794.375E+017 1300.000 −430.045 45.920 −502.285 4.778E+016 1400.000−435.631 42.474 −506.697 6.608E+015 1500.000 −439.948 39.964 −510.8111.120E+015

Example 4

Table 4 sets forth the thermodynamic analyses of methane using vanadiumpentoxide having the following reaction:2V₂O₅+CH₄(g)=2V₂O₃+CO₂(g)+2H₂O(g)

TABLE 4 T ΔH ΔS ΔG C kJ J/K kJ K 100.000 −137.042 343.602 −265.2571.363E+037 200.000 −135.690 346.825 −299.790 1.256E+033 300.000 −134.720348.700 −334.577 3.123E+030 400.000 −134.418 349.203 −369.484 4.714E+028500.000 −135.085 348.297 −404.371 2.099E+027 600.000 −137.027 345.953−439.095 1.863E+026 700.000 −268.714 207.807 −470.942 1.907E+025 800.000−273.724 202.905 −491.472 8.394E+023 900.000 −278.571 198.586 −511.5426.003E+022 1000.000 −283.213 194.788 −531.207 6.253E+021 1100.000−287.622 191.452 −550.515 8.777E+020 1200.000 −291.765 188.539 −569.5111.568E+020 1300.000 −295.604 186.016 −588.236 3.415E+019 1400.000−299.099 183.861 −606.727 8.774E+018 1500.000 −302.207 182.056 −625.0202.593E+018

Example 5

Table 5 sets forth the thermodynamic analyses of hydrogen utilizingmolybdenum trioxide in the following combustion reaction:MoO₃+H₂(g)=MoO₂+H₂O(g)

TABLE 5 T ΔH ΔS ΔG C kJ J/K kJ K 100.000 −86.121 24.017 −95.0832.047E+013 200.000 −87.311 21.189 −97.336 5.580E+010 300.000 −88.49818.914 −99.339 1.133E+009 400.000 −89.745 16.910 −101.128 7.046E+007500.000 −91.073 15.072 −102.726 8.726E+006 600.000 −92.482 13.359−104.147 1.702E+006 700.000 −93.966 11.751 −105.401 4.550E+005 800.000−95.510 10.241 −106.500 1.528E+005 900.000 −147.260 −37.779 −102.9393.835E+004 1000.000 −150.014 −40.034 −99.045 1.159E+004 1100.000−152.436 −41.867 −94.946 4.093E+003 1200.000 −154.520 −43.333 −90.6841.643E+003 1300.000 −156.254 −44.474 −86.291 7.335E+002 1400.000−157.630 −45.322 −81.799 3.580E+002 1500.000 −158.633 −45.906 −77.2351.886E+002

Example 6

Table 6 sets forth the thermodynamic analyses of hydrogen utilizing andvanadium pentoxide in the following reaction: V₂O₅+2H₂(g)=V₂O₃+2H₂O(g)

TABLE 6 T ΔH ΔS ΔG C kJ J/K kJ K 100.000 −152.746 80.031 −182.6093.667E+025 200.000 −154.375 76.159 −190.410 1.053E+021 300.000 −155.97373.096 −197.868 1.082E+018 400.000 −157.670 70.370 −205.040 8.164E+015500.000 −159.616 67.680 −211.943 2.090E+014 600.000 −161.967 64.827−218.570 1.193E+013 700.000 −228.966 −5.501 −223.613 1.008E+012 800.000−232.412 −8.874 −222.889 7.077E+010 900.000 −235.567 −11.687 −221.8567.569E+009 1000.000 −238.427 −14.028 −220.567 1.122E+009 1100.000−241.001 −15.976 −219.064 2.157E+008 1200.000 −243.289 −17.585 −217.3835.112E+007 1300.000 −245.288 −18.899 −215.557 1.439E+007 1400.000−246.993 −19.951 −213.612 4.671E+006 1500.000 −248.395 −20.765 −211.5741.711E+006

Tables 1 through 6 demonstrate that the reactions of the process of theinvention are thermodynamically favorable over a wide range oftemperatures as indicated by the negative ΔG values. The negative ΔHvalues show that the reactions are exothermic.

Reactions taking place during the first step of the process are complexand sometimes cannot be described with one reaction in such a widetemperature range (Tables 1-4). For example, at high temperatures,carbon monoxide will evolve as one of the products when reducingmolybdenum trioxide. Equilibrium composition for the reduction of MoO₃with carbon as a function of temperature is shown in FIG. 6. It can beseen from FIG. 6 that only up to 800° C. of the equilibrium compositionis described by the reaction shown in Table 1. Above that temperature,the CO content becomes tangible. It reaches almost 20% at 1500° C.

Example 7

Re-oxidation of the metal suboxides/metals is as critical as theoxidation of the fuel. The re-oxidation will be carried out in air, sothe oxygen potential in air (2.1 E-01 atm) must be greater than theequilibrium partial pressure of oxygen for the correspondingre-oxidation reaction. The temperature ranges in which the oxygenpotential in air is greater than that of the re-oxidation reaction canbe calculated.

The equilibrium partial pressure of oxygen as a function of temperaturefor the re-oxidation reaction of bismuth is given in Table 7. The Kcolumn represents the oxygen pressure. It can be seen from Table 7 thatthe temperature range in which bismuth can be re-oxidized with air isapproximately 100° C.-1500° C. in the reaction 0.667Bi₂O₃=1.333Bi+O₂(g).

TABLE 7 T ΔH ΔS ΔG C kJ J/K kJ K 100.000 384.602 178.070 318.1552.884E−045 200.000 383.379 175.165 300.500 6.648E−034 300.000 397.339200.706 282.304 1.861E−026 400.000 396.042 198.628 262.336 4.383E−021500.000 394.440 196.413 242.583 4.069E−017 600.000 392.541 194.107223.056 4.518E−014 700.000 390.344 191.729 203.764 1.153E−011 800.000367.765 169.272 186.111 8.719E−010 900.000 352.523 155.524 170.0702.673E−008 1000.000 346.251 150.393 154.778 4.459E−007 1100.000 340.010145.674 139.977 4.729E−006 1200.000 333.797 141.307 125.631 3.508E−0051300.000 327.612 137.244 111.706 1.953E−004 1400.000 321.452 133.44898.173 8.607E−004 1500.000 315.316 129.886 85.009 3.130E−003

Example 8

Table 8 sets forth the temperature ranges calculated for there-oxidation reactions listed in column 1 of the table according to thesame analysis carried out for bismuth in Example 7.

TABLE 8 Temperature Range Reaction (° C.) 2Na₂O + O₂ = 2Na₂O₂ 100-10002K₂O + O₂ = 2K₂O₂ 100-1200 2Rb₂O + O₂ = 2Rb₂O₂ 100-700  2Cs₂O + O₂ =2Cs₂O₂ 100-900  2BaO + O₂ = 2BaO₂ 100-700  2MnO + O₂ = 2MnO₂ 100-900 4TcO₂ + 3O₂ = 2Tc₂O₇ 100-1500 4ReO₂ + 3O₂ = 2Re₂O₇ 100-1500 OsO₂ + O₂ =OsO₄ 100-1500 Rh₂O + O₂ = Rh₂O₃ 100-800  2Pt + O₂ = 2PtO 100-500  2Pd +O₂ = 2PdO 100-700  2Cu + O₂ = 2CuO 100-1400 2Hg + O₂ = 2HgO 100-500 Tl₂O + O₂ = Tl₂O₃ 100-700  MoO₂ + O₂ = MoO₃ 100-1500 V₂O₃ + O₂ = V₂O₅100-1500 Pb + O₂ = PbO₂ 100-1100 4Bi + 3O₂ = 2Bi₂O₃ 100-1500

Example 9

In reference to the example systems, metal sub-oxides and/or metalsproduced in the first step of the process, will be re-oxidized in thesecond step according to the reactions shown in Tables 9 and 10. Table 8is a combustion reaction utilizing molybdenum trioxide with the formula2MoO₂+O₂(g)=2MoO₃.

TABLE 9 T ΔH ΔS ΔG C kJ J/K kJ K 100.000 −312.890 −141.309 −260.1602.637E+036 200.000 −312.395 −140.133 −246.091 1.480E+027 300.000−311.826 −139.046 −232.132 1.437E+021 400.000 −311.057 −137.814 −218.2878.708E+016 500.000 −310.037 −136.407 −204.575 6.643E+013 600.000−308.749 −134.843 −191.011 2.678E+011 700.000 −307.193 −133.158 −177.6103.421E+009 800.000 −305.381 −131.388 −164.382 1.004E+008 900.000−203.013 −36.357 −160.361 1.383E+007 1000.000 −198.490 −32.654 −156.9172.745E+006 1100.000 −194.498 −29.633 −153.808 7.101E+005 1200.000−191.067 −27.219 −150.970 2.257E+005

Example 10

Table 9 is a combustion reaction utilizing vanadium pentoxide with theformula: V₂O₃+O₂(g)=V₂O₅.

TABLE 10 T ΔH ΔS ΔG C kJ J/K kJ K 100.000 −332.386 −173.307 −267.7173.013E+037 200.000 −332.641 −173.913 −250.354 4.374E+027 300.000−332.849 −174.314 −232.941 1.703E+021 400.000 −332.877 −174.365 −215.5035.295E+016 500.000 −332.568 −173.943 −198.084 2.420E+013 600.000−331.747 −172.953 −180.734 6.501E+010 700.000 −266.158 −104.155 −164.8007.023E+008 800.000 −263.989 −102.032 −154.494 3.315E+007 900.000−261.966 −100.228 −144.383 2.687E+006 1000.000 −260.090 −98.693 −134.4393.283E+005 1100.000 −258.370 −97.391 −124.637 5.515E+004 1200.000−256.817 −96.299 −114.954 1.192E+004 1300.000 −255.447 −95.399 −105.3703.155E+003 1400.000 −254.277 −94.677 −95.868 9.844E+002 1500.000−253.323 −94.123 −86.429 3.518E+002

The data shown in Tables 8-10 demonstrate that oxidation of the metalsuboxides/metals with oxygen according to the process of the inventioncan be carried out in a flash furnace. The flash furnace will allowoperation of the process at temperatures higher than those of fluidizedbed or rotary kiln furnaces. Running the process at high temperaturewill significantly increase the rate of the chemical reaction and,therefore, the process throughput. The flash temperatures can becontrolled by modifying the reactor temperatures.

Examples 11 and 12

Examples 11 and 12 demonstrate that that the oxygen carriers in theprocess of the invention do not have to be completely cooled down toroom temperature after the reduction or oxidation. According to theinvention, they can be fed preheated into the next step of the reaction.This will facilitate the formation of a stronger sustainable flash andincrease the overall thermal efficiency of the process as a result ofreduced heat losses. The initial temperature of the oxygen carriers forsteps 1 and 2 was assumed to be 400° C. This temperature was used tocalculate the flash temperatures for the oxygen carriers, which are setforth in Tables 10 and 11. Tables 11 and 12 demonstrate that bothreactions of the process are exothermic and the heat energy released issufficient to create a stable flash.

TABLE 11 Reactor Flash Temperature Temperature Reaction (° C.) (° C.)CH₄ + 4Na₂O₂ = CO₂ + 4Na₂O + 2H₂O 400 1071 CH₄ + 4K₂O₂ = CO₂ + 4K₂O +2H₂O 400 740 CH₄ + 4Rb₂O₂ = CO₂ + 4Rb₂O + 2H₂O 400 1163 CH₄ + 4Cs₂O₂ =CO₂ + 4Cs₂O + 2H₂O 400 1032 H₂ + BaO₂ = BaO + H₂O 400 1834 CH₄ + 4MnO₂ =4MnO + CO₂ + 2H₂O 400 1073 1.5C + Tc₂O₇ = 2TcO₂ + 1.5CO₂ 400 2134 1.5C +Re₂O₇ = 2ReO₂ + 1.5CO₂ 400 1521 C + OsO₄ = OsO₂ + CO₂ 400 2499 C + Rh₂O₃= Rh₂O + CO₂ 400 1266 C + 2PtO = 2Pt + CO₂ 400 2093 4PdO + CH₄ = 4Pd +CO₂ + 2H₂O 400 1555 C + 2CuO = 2Cu + CO₂ 400 1085 C + 2HgO = 2Hg + CO₂400 2199 C + Tl₂O₃ = Tl₂O + CO₂ 400 1282 C + PbO₂ = Pb + CO₂ 400 1632C + 2MoO₃ = CO₂(g) + 2MoO₂ 400 771 C + V₂O₅ = CO₂(g) + V₂O₃ 400 7051.5C + Bi₂O₃ = 2Bi + 1.5CO₂ 400 318

TABLE 12 Reactor Flash Temperature Temperature Reaction (° C.) (° C.)2Na₂O + O₂ = 2Na₂O₂ 400 917 2K₂O + O₂ = 2K₂O₂ 400 1254 2Rb₂O + O₂ =2Rb₂O₂ 400 767 2Cs₂O + O₂ = 2Cs₂O₂ 400 909 2BaO + O₂ = 2BaO₂ 400 12252MnO + O₂ = 2MnO₂ 400 1994 4TcO₂ + 3O₂ = 2Tc₂O₇ 400 876 4ReO₂ + 3O₂ =2Re₂O₇ 400 1439 OsO₂ + O₂ = OsO₄ 400 721 Rh₂O + O₂ = Rh₂O₃ 400 18702Pt + O₂ = 2PtO 400 1316 2Pd + O₂ = 2PdO 400 1944 2Cu + O₂ = 2CuO 4002008 2Hg + O₂ = 2HgO 400 1675 Tl₂O + O₂ = Tl₂O₃ 400 1413 2MoO₂ + O₂ =2MoO₃ 400 1272 V₂O₃ + O₂ = V₂O₅ 400 1779 Pb + O₂ = PbO₂ 400 >3000 4Bi +3O₂ = 2Bi₂O₃ 400 3166

Example 13

It was calculated that when carbon is heated with molybdenum oxide to850° C., the flash temperature of the products will reach 1628° C. Attemperatures above 700° C., molybdenum trioxide exhibits a tangiblevapor pressure of various gaseous species (see FIG. 5). The existence ofa gaseous metal oxide oxygen carrier species radically improves the masstransfer capability of this system improving the reaction rate kineticsand reaction completion. It can be seen from FIG. 5 that molybdenumtrioxide creates tangible amounts of gaseous species during itsdecomposition at high temperatures; therefore, the fuel combustionreaction with MoO₃ at those temperatures will proceed mostly in thegaseous state.

Example 14

It was calculated that when methane is heated with molybdenum oxide to850° C., the flash temperature of the products will reach 1600° C. Whenthe reducing agent is also in the vapor phase, such as methane, thereaction will proceed very quickly to its full completion.

Examples 15 and 16

For the combustion of carbon and methane with vanadium pentoxide as theoxygen carrier, heating of the reagents to 700° C. leads to flashtemperatures of 1371° C. and 1361° C., respectively. The release ofenergy during the process of the examples can be used to bring the fuelcombustion processes to higher temperatures to form a stable flash. Theenthalpy change steeply increases (˜100%) at 900° C. for the combustionof fuel with molybdenum trioxide and at 700° C. for the combustion offuel with vanadium pentoxide. These steep enthalpy changes aredemonstrated in FIGS. 1, 2 and 4.

It will be apparent to those skilled in the art that various changes maybe made without departing from the scope of the invention which is notconsidered limited to the specific embodiments described in thespecification and drawings, but is only limited by the scope of theappended claims.

1. A process for chemical looping combustion comprising: (a) contactinga reduced oxygen carrier with oxygen to form an oxidized oxygen carrier,and (b) contacting said oxidized oxygen carrier and a fuel to producesaid reduced oxygen carrier and carbon dioxide, wherein both steps areexothermic.
 2. A process for chemical looping combustion in a furnacecomprising: (a) a first step wherein a reduced oxygen carrier iscontacted with oxygen to form an oxidized oxygen carrier, and (b) asecond step wherein an ash-containing fuel is contacted with saidoxidized oxygen carrier to produce a reaction product comprising saidreduced oxygen carrier, carbon dioxide and fly ash, wherein both thefirst step and the second step are exothermic.
 3. A process for chemicallooping combustion comprising the steps of: (c) contacting at least onereduced oxygen carrier with oxygen in a first reactor to form at leastone oxidized oxygen carrier, (d) passing the at least one oxidizedoxygen carrier from said first reactor to a second reactor receivablyconnected to said first reactor, (e) contacting said at least oneoxidized oxygen carrier with at least one fuel in said second reactor toproduce said at least one reduced oxygen carrier and carbon dioxide, and(f) passing said at least one reduced oxygen carrier from said secondreactor to said first reactor, wherein both reaction steps areexothermic.
 4. A process for chemical looping combustion in a flashfurnace, said flash furnace comprising a first reactor and a secondreactor receivably connected to said first reactor, said processcomprising the steps of: (a) feeding oxygen and a reduced oxygen carrierinto the first reactor having a first reactor temperature at a locationthat is not a reaction zone, said oxygen and said reduced oxygen carriereach having a temperature that is lower than said first reactortemperature, and said first reactor temperature being sufficient toignite the oxygen and the reduced oxygen carrier as they pass throughthe first reactor and create a reaction that is sufficiently exothermicto form a self-sustaining reaction zone having a first flashtemperature, said reaction producing an oxidized oxygen carrier; (b)feeding said oxidized oxygen carrier and a fuel into said second reactorat a location that is not a reaction zone having a second reactortemperature, said oxidized oxygen carrier and said fuel each having atemperature that is lower than said second reactor temperature, and saidreactor temperature being sufficient to ignite the oxidized oxygencarrier and the fuel as they pass through the second reactor and createa reaction that is sufficiently exothermic to form a self-sustainingreaction zone having a second flash temperature, said reaction producingthe reduced oxygen carrier and carbon dioxide; and (c) optionally,feeding said reduced oxygen carrier from said second reactor to saidfirst reactor.
 5. A process for chemical looping combustion comprisingthe steps of: (g) feeding a reduced oxygen carrier and oxygen into afirst reactor; (h) contacting the reduced oxygen carrier with the oxygensource in said first reactor to form an oxidized oxygen carrier; (i)passing the oxidized oxygen carrier from said first reactor to a secondreactor receivably connected to said first reactor; (j) feeding a fuelinto said second reactor for contact with said oxidized oxygen carrierwithin said second reactor to produce a reaction product comprising saidreduced oxygen carrier, carbon dioxide and carbon monoxide; and (k)passing said reduced oxygen carrier from said second reactor to saidfirst reactor; wherein the reaction in the first reactor and thereaction in the second reactor are both exothermic.
 6. The process ofclaim 4 wherein the fuel is an ash-containing fuel and wherein thereaction in the second reactor further produces fly ash.
 7. The processof claim 4 wherein the reduced oxygen carrier and the oxygen arepreheated before being fed into the first reactor of the furnace.
 8. Theprocess of claim 4 wherein the fuel and the oxidized oxygen carrier arepreheated before being fed into the second reactor of the furnace. 9.The process of claim 3 wherein the oxygen and the reduced oxygen carrierare fed into the first reactor at a rate that is substantially constantand the first reactor temperature and the second reactor temperatureremain substantially constant.
 10. The process of claim 4, wherein afterstep (b), the fuel and the oxidized oxygen carrier are blended prior tobeing passed into the second reactor.
 11. The process of claim 1 orclaim 2 wherein said process is performed in a flash furnace.
 12. Theprocess of claim 1 wherein said process is performed in a rotary kiln, amultiple hearth furnace, a vertical tube furnace or a fluidized bedreactor.
 13. The process of claim 1 wherein said process is continuous.14. The process of claim 1 further comprising recycling the reducedoxygen carrier produced during said second step into said first step ofthe process.
 15. The process of claim 1 further comprising the step ofseparating and sequestering the carbon dioxide produced during thesecond step.
 16. The process of claim 2 wherein at least a portion ofthe reduced oxygen carrier together with at least a portion of the flyash are removed from the furnace.
 17. The process of claim 16 whereinthe amount of reduced oxygen carrier is fed into the furnace in anamount that is substantially the same as the amount of reduced oxygencarrier being removed from the furnace.
 18. The process of claim 2wherein at least a portion of the reduced oxygen carrier together withat least a portion of the fly ash are removed from the furnace andsubsequently utilized as a ferroalloy addition in a process to producean alloy material containing iron and slag.
 19. The process of claim 5further comprising the step of separating the carbon monoxide producedduring the second step.
 20. The process of claim 1 or claim 2 whereinthe reduced oxygen carrier is a metal or a metal suboxide.
 21. Theprocess of claim 1 wherein the reduced oxygen carrier is a metalselected from the group consisting of rhenium, platinum, rhodium,palladium, copper, barium, manganese, molybdenum, vanadium, bismuth,lead, mercury, sodium, potassium, rubidium, and cesium.
 22. The processof claim 2 wherein the oxygen carrier is substantially free-flowing. 23.The process of claim 1 wherein the fuel is selected from carbon, coal,hydrogen, hydrocarbon, biofuel, methane, natural gas, petroleum, crudeoil, tar sands, oil shale, biomass, algae, fuel-rich waste gases fromfuel cells, other fossil fuel or synthetic fuel.
 24. The process ofclaim 2 wherein the ash-containing fuel is coal.
 25. The process ofclaim 1 wherein the fuel is a carbon, a hydrocarbon, or hydrogen in theform of a solid, a liquid or a gas.
 26. The process of claim 1 whereinthe oxygen carrier is in the form of a powder.
 27. The process of claim26 wherein the oxygen carrier powder has a particle size of from 100nanometers to 1 mm as determined by laser light scattering.
 28. Theprocess of claim 1 wherein the oxygen carrier is in the form of a powderhaving a particle size of from 20 microns to 250 microns as determinedby laser light scattering.
 29. The process of claim 1 wherein the fuelis a coal in the form of a powder.
 30. The process of claim 29 whereinthe coal powder has a particle size of from 100 nanometers to 10 mm asdetermined by laser light scattering.
 31. The process of claim 1 whereinthe fuel is a coal in the form of a powder having a particle size offrom 20 microns to 250 microns as determined by laser light scattering.32. The process of claim 1 wherein the fuel is coal having a particlesize that is substantially similar to the particle size of the oxygencarrier.
 33. The process of claim 1 wherein said oxidized oxygen carrieris at least partially vaporized during said second step of the process.34. The process of claim 4 wherein the difference between said firstreactor temperature and said first flash temperature in the firstreactor is at least 300° C.
 35. The process of claim 4 wherein thedifference between said second reactor temperature and said second flashtemperature in the second reactor is at least 300° C.
 36. The process ofclaim 4 wherein the difference between said first reactor temperatureand said first flash temperature in the first reactor is at least 800°C.
 37. The process of claim 4 wherein the difference between said secondreactor temperature and said second flash temperature in the secondreactor is at least 800° C.
 38. The process of claim 4 wherein thereduced oxygen carrier and the oxygen are fed into the first reactor ata rate sufficient to substantially off-set the heat loss of the firstreactor and create a stable self-sustaining reaction zone within thefirst reactor.
 39. The process of claim 4 wherein the oxidized oxygencarrier and the fuel are fed into the second reactor at a ratesufficient to substantially off-set the heat loss from the secondreactor and create a stable self-sustaining reaction zone within thesecond reactor.
 40. The process of claim 2 wherein the temperaturewithin the first reactor is above the solid/liquid phase transitiontemperature of the reduced oxygen carrier.
 41. The process of claim 2wherein the temperature within the first reactor is above the solid/gasphase transition temperature of the reduced oxygen carrier.
 42. Theprocess of claim 2 wherein the temperature within the first reactor isabove the liquid/gas phase transition temperature of the reduced oxygencarrier.
 43. The process of claim 2 wherein the temperature within thesecond reactor is above the solid/liquid phase transition temperature ofthe oxidized oxygen carrier.
 44. The process of claim 2 wherein thetemperature within the second reactor is above the solid/gas phasetransition temperature of the oxidized oxygen carrier.
 45. The processof claim 2 wherein the temperature within the second reactor is abovethe liquid/gas phase transition temperature of the oxidized oxygencarrier.
 46. The process of claim 3 wherein the residence time of theoxygen and the reduced oxygen carrier in the first reactor is from 0.01to 1.0 minute.
 47. The process of claim 3 wherein the residence time ofthe oxygen and the reduced oxygen carrier in the first reactor is from0.01 to 10 seconds.
 48. The process of claim 3 wherein the process isperformed in a flash furnace and the residence time of the fuel and theoxidized oxygen carrier in the second reactor is from 0.01 seconds to1.0 minute.
 49. The process of claim 3 wherein the process is performedin a flash furnace and the residence time of the fuel and the oxidizedoxygen carrier in the second reactor is from 0.01 seconds to 10 seconds.50. The process of claim 4 wherein the reduced oxygen carrier flowsconcurrently in the same direction with the flow of the oxygen in thefirst reactor.
 51. The process of claim 4 wherein the oxidized oxygencarrier flows concurrently in the same direction with the flow of thefuel in the second reactor.
 52. The process of claim 5 wherein the fueland the oxidized oxygen carrier are fed into the second reactor insubstantially stoichiometric amounts.
 53. The process of claim 5 whereinthe fuel and the oxidized oxygen carrier are fed into the second reactorin less than stoichiometric amounts in order to produce carbon monoxide.54. A process for generating useful work comprising the process ofclaim
 1. 55. A process for generating useful work comprising the firststep of the process of claim
 1. 56. A process for generating useful workcomprising the second step of the process of claim
 1. 57. The process ofclaim 1 further comprising utilizing the energy produced during theexothermic process in a generator for generating electricity.
 58. Theprocess of claim 1 further comprising converting the energy producedduring the exothermic process into steam that is used to rotate aturbine engine.
 59. The process of claim 1 wherein the steps can beperformed in either order.
 60. The process of claim 4 further comprising(d) feeding carbon dioxide into said second reactor.